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Lysosomes are vital organelles vulnerable to injuries from diverse materials. Failure to repair or sequester damaged lysosomes poses a threat to cell viability. Here we report that cells exploit a sphingomyelin-based lysosomal repair pathway that operates independently of ESCRT to reverse potentially lethal membrane damage. Various conditions perturbing organelle integrity trigger a rapid calcium-activated scrambling and cytosolic exposure of sphingomyelin. Subsequent metabolic conversion of sphingomyelin by neutral sphingomyelinases on the cytosolic surface of injured lysosomes promotes their repair, also when ESCRT function is compromised. Conversely, blocking turnover of cytosolic sphingomyelin renders cells more sensitive to lysosome-damaging drugs. Our data indicate that calcium-activated scramblases, sphingomyelin, and neutral sphingomyelinases are core components of a previously unrecognized membrane restoration pathway by which cells preserve the functional integrity of lysosomes.

Significance The acyl chain composition of Chlamydomonas triacylglycerols (TAGs) suggests that they are assembled from prokaryotic precursors, proposed to be synthesized in the chloroplast. However, in most eukaryotes, the endoplasmic reticulum (ER) appears to be the main organelle for storage TAG biosynthesis. Interestingly, Chlamydomonas reinhardtii has a distinct lysophosphatidic acid acyltransferase that localizes to the ER but resembles prokaryotic lysophosphatidic acid acyltransferases (LPAATs) in its substrate preference. Thus, Chlamydomonas and related green algae, unlike land plants, can synthesize “prokaryotic” acyl-lipids in the ER, with intriguing implications for biotechnological applications.

The GaP crystal quality and Si bulk lifetime of GaP/Si heterostructures, grown by molecular beam epitaxy, are investigated. The Si bulk lifetime is reduced by over one order of magnitude after thermal deoxidation at high temperatures (>700 °C). This significant reduction of the bulk lifetime is not observed when 150 nm-thick SiN x film is present on the backside of Si wafer, which can act as a diffusion barrier and/or getter. In addition, a 15 nm-thick GaP layer grown on the front side of Si wafer with SiN x on the backside shows a high crystal quality of GaP with a low crystalline defect density of 1.1 × 10 5 cm −2 . Moreover, the Si bulk lifetime is determined to be 1.83 ms with a-Si:H passivation at an injected minority-carrier density of 1 × 10 15 cm −3 , indicative of no bulk lifetime degradation. The high crystallinity of GaP and improved Si bulk lifetime are beneficial to improve photovoltaic device performance of III–V compound solar cells integrated with Si solar cells.

Eco-friendly acrylic resin/clay nanocomposites containing pristine montmorillonite (PM) or modified clays (30B and 25A) were prepared from acrylic and styrenic monomers using non-aqueous dispersion (NAD) polymerization. Effect of nanoclays on physical properties of polymerization product and resulting nanocomposites was investigated. In view of NAD particle stability, addition of nanoclay at the beginning of polymerization is proved to be good. Results of gel fraction, acid value and viscosity of the NAD product showed that nanocomposites containing clay 25A showed better physical properties than the ones with other clays. GPC results exhibit the increase in molecular weight and decrease in polydispersity index for the 25A nanocomposite. Increase in layer distance confirmed from XRD analysis showed good dispersion of 25A in the nanocomposite. Thermal and dynamic mechanical analysis showed that highest glass transition temperature and storage modulus for 25A nanocomposites. These results indicate that 25A nanoclay gives the best properties in the process of non-aqueous dispersion polymerization of acrylic resin/nanoclay nanocomposites.

In many eukaryotes, endoplasmic reticulum (ER) stress activates the unfolded protein response (UPR) via the transmembrane endoribonuclease IRE1 to maintain ER homeostasis. The ER stress response in microalgae has not been studied in detail. Here, we identified Chlamydomonas reinhardtii IRE1 (CrIRE1) and characterized two independent knock-down alleles of this gene. CrIRE1 is similar to IRE1s identified in budding yeast, plants, and humans, in terms of conserved domains, but differs in having the tandem zinc-finger domain at the C terminus. CrIRE1 was highly induced under ER stress conditions, and the expression of a chimeric protein consisting of the luminal N-terminal region of CrIRE1 fused to the cytosolic C-terminal region of yeast Ire1p rescued the yeast ∆ire1 mutant. Both allelic ire1 knock-down mutants ire1-1 and ire1-2 were much more sensitive than their parental strain CC-4533 to the ER stress inducers tunicamycin, dithiothreitol and brefeldin A. Treatment with a low concentration of tunicamycin resulted in growth arrest and cytolysis in ire1 mutants, but not in CC-4533 cells. Furthermore, in the mutants, ER stress marker gene expression was reduced, and reactive oxygen species (ROS) marker gene expression was increased. The survival of ire1 mutants treated with tunicamycin improved in the presence of the ROS scavenger glutathione, suggesting that ire1 mutants failed to maintain ROS levels under ER stress. Together, these results indicate that CrIRE1 functions as an important component of the ER stress response in Chlamydomonas, and suggest that the ER stress sensor IRE1 is highly conserved during the evolutionary history.

Summary Despite a strong interest in microalgal oil production, our understanding of the biosynthetic pathways that produce algal lipids and the genes involved in the biosynthetic processes remains incomplete. Here, we report that Chlamydomonas reinhardtii Cre09.g398289 encodes a plastid‐targeted 2‐lysophosphatidic acid acyltransferase (CrLPAAT1) that acylates the sn‐2 position of a 2‐lysophosphatidic acid to form phosphatidic acid, the first common precursor of membrane and storage lipids. In vitro enzyme assays showed that CrLPAAT1 prefers 16:0‐CoA to 18:1‐CoA as an acyl donor. Fluorescent protein‐tagged CrLPAAT1 was localized to the plastid membrane in C. reinhardtii cells. Furthermore, expression of CrLPAAT1 in plastids led to a > 20% increase in oil content under nitrogen‐deficient conditions. Taken together, these results demonstrate that CrLPAAT1 is an authentic plastid‐targeted LPAAT in C. reinhardtii, and that it may be used as a molecular tool to genetically increase oil content in microalgae.

In this study, we demonstrate InAs/GaAs submonolayer quantum dots (SQDs) with no wetting layer (WL) formed by using the self-assembling technique. An evolutional feature was observed in the photoluminescence spectra taken from QDs whose coverages were in the range from submonolayer to a few monolayer (0.5–2.5 ML). The QD samples revealed that a small number of conventional QDs (CQDs) with a WL coexisted with the majority of SQDs with no WL. Multipeak spectra were gradually changed to single-peak profiles, and an abrupt transition from SQDs to CQDs arose before and after WL formation. A single-mode SQD ensemble was achieved by 1.5 ML, for which the coverage was close to that of the WL (1.7 ML) in which the strain field was nearly uniform over the entire layer. This showed that the sublevel of SQDs (1.32 ± 0.1 eV) was much closer to the GaAs band edge than that of CQDs (∼1.2 eV).

We report the spectral response characteristics of a dual–band infrared photodetector based on nBn photodiode configuration–with GaSb and InGaAsSb absorption layers and a ternary layer of AlGaSb that serves as unipolar barrier in between—which has independent access to both sides. The resulting structure has detection capability in the short-wavelength infrared ranges, cut-off wavelength of 1.6 μm (SWIR1; GaSb) and 2.65 μm (SWIR2; InGaAsSb) depending on the applied bias. The dual-band photodetector was evaluated by current–voltage (I–V) characteristics, spectral response, and detectivity (D*). The measured values of D* at 300 K were 2.3 × 1012 cm·Hz1/2·W−1 (at 1.5 μm) and 2.1 × 1011 cm·Hz1/2·W−1 (at 2.25 μm).

Bat-like InN nanostructures were successfully grown on GaN/AlN/Si(1 1 1) substrates using molecular beam epitaxy method. The initial growth behavior and structural properties of InN nanobats were studied from a nanostructural point of view. During the initial stage of the growth, a nucleation process and a shape-decision process took place in which 3-dimensional (3-D) GaN nanoislands and nanorods were formed on AlN initiation layer/Si substrate. This was followed by the independent growth of 3-D InN nanoislands and nanorods. Lateral expansion of the InN nanobats was observed, and the diameter of InN bats then reached a fixed value.

The structural properties of the InAs QDs embedded in the InGaAsSb layers with varying In content of 3, 7, and 9 % have been investigated by x-ray diffraction. The In incorporation increases the in-plane and out-of-plane strain of the InGaAsSb in the structures. The density of crystalline defects is increased when the In content of 3 % is incorporated. However, the further increase of In content to 7 and 9 % leads to the decrease of the defect density as a result of the reduced lattice mismatch between the InAs QDs and InGaAsSb layers.

Single-junction GaAs-based solar cell structures are grown by metalorganic chemical vapor deposition system at the growth rates of 14 µm/hr and 56 µm/hr. The X-ray diffraction study reveals that the crystal quality of the structures with varying the growth rates is comparable. From the external quantum efficiency spectra, it is observed that different behaviors exist in the short wavelengths ( 500 nm) as the growth rate increases. The short-circuit current densities of the standard and fast grown cells are comparable. However, the open-circuit voltage of the fast grown cell is lower by above 40 mV as a result of the reduced minority carrier lifetime in the base layer, which is estimated by PC1D simulation.

The optical properties of the Stranski–Krastanov (S–K) grown InAs/GaAsSb quantum dots (QDs) coupled to sub-monolayer (SML) InAs QD stacks are investigated using photoluminescence (PL) spectroscopy. The PL emission peak of the S–K QDs shifts to shorter wavelengths with increasing the number of SML stacks (NSML) due to the increasing strain fields from the SML QDs. The PL peak energy is linearly increased with increasing the cube root of excitation power, with a different ratio of the absorption coefficient to radiative recombination rate for all the QD samples. The total carrier lifetime for the S–K QDs is increased with increasing NSML, most probably caused by the increase in the ground-state transition energy of the S–K QDs. The nonmonotonic behavior of the thermal activation energy of electrons in the S–K QDs is observed due to the NSML-dependent variation of the strain and Coulombic interaction within the QDs.

The impact of the Sb composition on the structural and optical properties of ten-stack InAs/GaAsSb quantum dots (QDs) were investigated using transmission electron microscopy (TEM), high-resolution x-ray diffraction (XRD), and photoluminescence (PL). The TEM images demonstrate that the Sb composition affects the change in the QD density and morphology. From analysis of XRD reciprocal space maps (RSMs) of the (224) asymmetrical reflection, it is found that as the Sb composition increases the relaxation of the initial elastic stress of the GaAsSb increases up to 23 %. In addition, the Sb composition influences the interband optical transitions such as the PL peak redshift and carrier lifetimes.

The optical properties of InAs quantum dots (QDs) embedded in a GaAsSb matrix with different delta (δ)-doping levels of 0, 2, 4, and 6 electrons per dot (e−/dot), incorporated to control the occupation of QD electronic states, are studied by photoluminescence (PL) spectroscopy. The time-resolved PL data taken at 10 K reveal that the increase of δ-doping density from 2 to 6 e−/dot decreases the recombination lifetime of carriers at ground states of the QDs from 996 ± 36 to 792 ± 19 ps, respectively. Furthermore, the carrier lifetime of the sample with 4 e−/dot is found to increase at a slower rate than that of the undoped sample as temperature increases above 70 K. An Arrhenius plot of the temperature dependent PL intensity indicates that the thermal activation energy of electrons in the QDs, required for carrier escape from the dot ground state to continuum state, is increased when the δ-doping density is high enough (>4 e−/dot). These results are attributed to the enhanced Coulomb interaction of electrons provided by the δ-doping, leading to reduced thermal quenching of the PL.

We investigate the structural and optical properties of InAs quantum dots (QDs) embedded in In x Ga1−x As0.96Sb0.04 layers with different In content. Indium incorporation from 0 to 9% increases QD areal density up to 9.3 × 1010 cm−2 and decreases QD diameter and height by the reduction of the island–island interaction. The elastic strain of the InGaAsSb layers, surrounded by a GaAs matrix, increases with higher In content. Further, the increase of In content from 5 to 9% reduces the density of dislocation loops in the InGaAsSb and GaAs layers almost by half due to improvement of the InAs/InGaAsSb interface quality. The photoluminescence peak from the QDs is redshifted with increasing In content as a result of reduced strain inside the QDs.

The structural characteristics and device performance of strain-compensated InAs/GaAsSb quantum dot solar cells (QDSCs) with different GaP coverages have been studied. The in-plane (out-of-plane) compressive strain of the QD stacks is reduced from −1.24 (+1.06) to −0.39 (+0.33)% by increasing the GaP coverage from 0 to 4 ML. This strain compensation decreases strain-induced dislocation density and hence enhances the overall crystal quality of the QDSCs. The external quantum efficiency spectra reveal that the increase in the GaP coverage increases the photocurrent from wavelengths shorter than GaAs bandedge of 880 nm, while it decreases the photocurrent from near infrared wavelengths beyond the bandedge. The conversion efficiency of the QDSCs is significantly improved from 7.22 to 9.67% as the GaP coverage is increased from 0 to 4 ML.

The structural and optical properties of ten-stack InAs/GaAsSb quantum dots (QDs) with different spacer layer thicknesses (ds = 2, 5, 10, and 15 nm) are reported. X-ray diffraction analysis reveals that the strain relaxation of the GaAsSb spacers increases linearly from 0% to 67% with larger ds due to higher elastic stress between the spacer and GaAs matrix. In addition, the dislocation density in the spacers with ds = 10 nm is lowest as a result of reduced residual strain. The photoluminescence peak energy from the QDs does not change monotonically with increasing ds due to the competing effects of decreased compressive strain and weak electronic coupling of stacked QD layers. The QD structure with ds = 10 nm is demonstrated to have improved luminescence properties and higher carrier thermal stability.

We have studied the material and photovoltaic characteristics of InAs/GaAsSb sub-monolayer quantum dot solar cells (QDSCs) with different Sb contents of 0%, 5%, 15%, and 20%. All QDSCs exhibit an extended external quantum efficiency (EQE) response in the wavelength range of 960–1000 nm that corresponds to sub-bandgap photon absorption. As Sb content increases from 5% to 20%, the cutoff wavelength in the EQE extends towards longer wavelength whilst the EQE in the wavelength region of 300–880 nm is lowered due to increased defect density. Compared to the QDSC (Sb 0%), an Sb incorporation of 5% enhances the short-circuit current density from 20.65 to 22.15 mA/cm2 induced by Sb surfactant effect. Since the open-circuit voltage and fill factor of the QDSC (Sb 5%) are comparable to those of the QDSC (Sb 0%), an enhancement in solar cell efficiency (10.5%) of the QDSC (Sb 5%) is observed. Further increasing Sb content to 15% and 20% results in the degradation of solar cell performance due to increased nonradiati...

The structure-performance properties of single-layered and multi-layered InAs/GaAs1−xSbx quantum dot (QD) system, grown by molecular beam epitaxy on GaAs (001) substrates, have been investigated as a function of Sb concentration. Electron microscopy observations showed no significant crystalline defects for the single-layered InAs QDs (Sb 20%). X-ray diffraction analysis revealed that the increase of Sb concentration from 7.3% to 10.2% for the multi-layered QDs increased the strain relaxation from 0% to ∼23% and the dislocation density of GaAsSb layers went up to 3.6 × 109 cm−2. The peak energy of QD luminescence was red-shifted with increasing Sb concentration due to reduced strain inside QDs. Moreover, the carrier lifetime of the QDs was highly improved from 1.7 to 36.7 ns due to weak hole confinement as the Sb concentration was increased from 7.3% to 10.2%. These structures should be highly promising as the basis for photovoltaic solar-cell applications. Finally, the increased Sb concentration increase...

We have studied the material properties and device performance of InAs/GaAs quantum dot solar cells (QDSCs) made using three different QD growth modes: Stranski-Krastanov (S-K), quasi-monolayer (QML), and sub-monolayer (SML) growth modes. All QDSCs show an extended external quantum efficiency (EQE) at near infrared wavelengths of 950–1070 nm from the QD absorption. Compared to the S-K and SML QDSCs, the QML QDSC with a higher strain exhibits a poor EQE response in the wavelength region of 300–880 nm due to increased non-radiative recombination. The conversion efficiency of the S-K and SML QDSCs exceeds that of the reference cell (13.4%) without QDs due to an enhanced photocurrent (>16% increase) produced by the silicon doped QD stacks. However, as expected from the EQE of the QML QDSC, the increase of strain-induced crystalline defects greatly degrades the photocurrent and open-circuit voltage, leading to the lowest conversion efficiency (8.9%).

We studied the optical properties of InAs/GaAs0.83Sb0.17 quantum dots (QDs), with varying silicon delta-doping position (spatial distance, d = 0.5, 1, and 2 nm), using photoluminescence (PL) measurements. Compared with the undoped QDs, the PL peak energies of the ground state (GS) emissions for the doped QDs with d = 0.5 and 2 nm were found to be greatly blueshifted by ∼31 meV, which was much larger than that for the doped QDs with d = 1 nm. The radiative recombination rate of the GS emissions for the doped QDs with d = 1 nm was estimated to be slower than that for the other doped QDs at 10 K. The doped QDs with d = 1 nm showed the fastest redshift of the GS peak energy with temperature and lowest thermal activation energy (151 meV) of electrons among the QD samples. Further, the time-resolved PL data revealed that the average carrier lifetime (6.3 ns) in the doped QDs with d = 1 nm was longer even than that in the undoped QDs (5.5 ns) because of the weakened electron-hole wavefunction overlap by the V-shaped potential barrier in the doped QDs.

Coherent electron microdiffraction patterns have been obtained from a new crystalline precipitate found in silicon wafers annealed at 635 °C for 256 h. On the basis of the experimental evidence presented, the most likely structure is that of keatite (SiO2, tetragonal). The implications for the study of oxygen precipitation in silicon are discussed.

Evidence for a new microcrystalline precipitate in CZ Si annealed for 256 hrs at 635°C is presented by electron microdiffraction. This may be a precursor phase for the formation of amorphous platelets [9]. Multiple scattering microdiffraction calculations which distinguish the symmetries of two models for the thermal donor are also given.